The present invention relates to an improved piano construction for enriched stereophonic tonal radiation, and more particularly relates to improvement in the construction of a board or boards defining the front side of the resonant cavity of an upright type piano for enriched tonal radiation into atmospheric spaces in front of the piano.
A casing for an upright type piano functions as a kind of resonance box having a cavity defined by a top board, a pair of sides, a front board and a bottom board and the back side of the box is closed by a sound board over which a number of strings are arranged in a tightly stretched state. As a string is struck, vibration of the string is transmitted to the sound board via a bridge arranged on the sound board in order to support the string. Vibration of the sound board so caused generates corresponding atmospheric vibration within the cavity which is perceived as a tone by the audience. In this tone generating mechanism, the cavity resonance, i.e. the above-described atmospheric vibration within the cavity, plays an important role in obtaining a beautiful acoustic effect.
Usually, an upright type piano is placed in a room with the back side very close to a wall of the room. Therefore, although the sound board is exposed on the back side of the piano, the back side of the cavity is in most cases actually closed by the wall surface. In other words, the resonant cavity is actually of a completely closed construction and the tones are apt to be confined in this closed resonant cavity. Such complete tonal confinement tends to cause biased resonance of the cavity to tones of particular frequencies only, which seriously degrades the tone quality of the piano.
In one conventional proposal for releasing such tonal confinement, a relatively large screen is formed in the lower front board in order to enable forward radiation of the tones. However, presence of such a large opening in the board of the casing often results in very poor resonance of the cavity and generation of noises at striking of strings, both leading to generation of deteriorated musical tones.
In another conventional proposal for mitigating such tonal confinement a relatively small opening is formed on the front side of the resonant cavity by opening a music rack arranged above the keyboard. However, presence of such a small opening in the front board of the casing cannot actually assure sufficient balanced radiation of tones over all tone ranges.
In both conventional examples further, it is quite impossible to freely select the tonal radiation, the tonal radiation therefore lacks in directivity and the acoustic effect of the tones generated by the piano is rather monophonic.